1. Field of the Invention
The present invention relates to a semiconductor substrate and a method for producing the substrate which is constituted as an SOI (Silicon On Insulator) structure or the similar structure and which substrate is used in various semiconductor integrated circuit devices.
The producing method of the present invention especially relates to one which is called a recrystallization method.
The semiconductor substrate of the present invention is applicable to and can be used in various devices such as a high integrated LSI device, a high pressure resisting device and a three-dimensional integrated circuit.
The SOI structure includes the structure in which the semiconductor single crystal film to be grown is made from a compound semiconductor such as GaAs other than silicon. That is, the present invention is not limited to the structure in which the semiconductor single crystal film is made from silicon.
2. Description of the Related Art
An SOI structure has been proposed in which a semiconductor film is grown on a dielectric film or substrate.
The SOI structure is fabricated by various techniques such as a recrystallization method, an epitaxial growing method, an insulation layer burying method and a lamination method. Such techniques are explained in general in "Techniques for forming SOI structure" (published from Sangyo Tosho Co. Ltd., 1987).
Among the recrystallization methods, in accordance with a laser beam recrystallization method, the crystal is grown in such a way that a polycrystalline film or an amorphous film is formed on an insulation film base then the film is molten by energy of a laser beam and after that the molten film is recrystallized while the location of the molten portion is being changed.
In the above mentioned laser beam recrystallization method, various attempts have been tried in order to obtain a single crystal film by improving the temperature distribution in the polycrystalline or amorphous film as exemplified below.
(a) A method in which an optical system or a plurality of laser beam sources are used so as to even the temperature distribution in the laser beam spot.
(b) A method in which an optical absorbent film or an antireflection film is disposed on a surface of a sample in order to change the absorbent ratio of the laser beam incident upon the sample so as to even the temperature distribution over the sample.
(c) A method in which the structure of the sample is changed so that the heat radiation ratio of the sample is spatially changed so as to even the temperature distribution over the sample.
However, even though the above mentioned methods are adopted, it becomes only possible to partially grow the single crystal in the sample and it is still difficult to grow the single crystal over the entire area of the sample.
Also, Japanese Patent Publication (KOKOKU) No. 62-40858 discloses a semiconductor device. However, the disclosed device has a large junction capacitance which impedes the functional speed of the device.